Scattered along tropical sea floors, cone snails sit cloaked in funnel-shaped shells. But under an unassuming coating of coral and algae lies a hidden talent.
When a cone snail detects an appetizing fish swimming by, it shoots out a venom-tinged harpoon packed with thousands of molecules to help it incapacitate and hunt its prey. The fish is paralyzed, and the snail can reel in its lunch.
Bea Ramiro, a biochemistry graduate student at the University of Copenhagen, remembers seeing the occasional abandoned shell on the beach during her childhood in the Philippines, but she didn’t know who its former tenant was or the formidable arsenal it wielded until, as a college student, she heard a talk given by Baldomero Olivera, a biochemist at the University of Utah.
Olivera, also Filipino, had been inspired to study cone snails by his own childhood encounters with their shells (1). To him, they were more than just cunning marine predators: Like many other venomous creatures, they were laboratories synthesizing thousands of chemicals designed by nature itself. Some of these molecules had an especially intriguing function: they could blunt pain in humans.
For years, venomous snails, scorpions, and spiders have offered promising starting points for developing opioid-free pain relievers. In an early success, Olivera discovered a pain-blocking cone snail peptide that became the drug Prialt, which was approved by the Food and Drug Administration for treating severe chronic pain in 2004. Since then, technologies have matured, allowing researchers like Ramiro, who is now investigating her own cone snail peptide, to more quickly and comprehensively characterize the molecular makeup of venom.
“It seems the time is right to begin to harvest our understanding of venoms and these exotic peptides we’ve isolated from venoms,” said Bruce Hammock, an entomologist at the University of California, Davis.
Nature outwits pain
More than one fifth of Americans report chronic pain, making it one of the largest unmet medical needs today. But it’s also a challenging target for drug development.
“It's a high risk indication because so many companies have failed,” Hammock said.
For starters, experiencing pain is important for survival. It’s what keeps us from burning our hands on the stove or from walking on a sprained ankle. Potential dangers like these activate neurons that send a pain signal to the brain. But when neurons malfunction, this alarm system can become constant and debilitating.
Existing medications are often insufficient for treating chronic pain, or they pose risks for addiction or tolerance. Opioid pain relievers have resulted in opioid use disorders in more than 1 million Americans and led to tens of thousands of deaths in 2019 alone.
There is not only one way to cause or experience pain. It can arise from inflammation, sensory stimuli, or neuronal damage, so there isn’t a single treatment that works for all people experiencing pain. Pain relievers often target pathways or receptors involved in transmitting the pain signal such as inflammatory molecules or the “orchestra of ion channels” on the surface of neurons that control whether the neuron propagates a signal, said Vladimir Yarov-Yarovoy, an ion channel biologist at the University of California, Davis.
That makes it tricky to design the perfect molecule, but that’s where nature-made venoms can help. Take NaV1.7, for example, a sodium ion channel that is often found on pain-transmitting neurons. In the early 2000s, Merck researchers discovered that a peptide toxin from tarantula venom binds perfectly to inactivate NaV1.7 (2).
“The idea that the venoms of hunting animals are full of ion channel modulators is very old,” said Heike Wulff, a pharmacologist at the University of California, Davis. Hunters prefer prey that doesn’t put up a fight. Targeting sodium and calcium channels that mediate pain and motor neuron signaling can immobilize prey and keep them from reacting to the pain of an attack. Venom peptides can also play defensive roles, deterring other predators in search of their next meal.
Despite their common goal, venoms are as varied as the animals that produce them. There are around 1,000 species of cone snails, for example, and each makes its own armamentarium of hundreds of peptides that might incapacitate potential prey or predators. Wulff described it as a form of combinatorial chemistry happening as the venom gland generates a diverse array of peptides. Scientists have leveraged this range in the laboratory; early studies characterized ion channels based on the venoms they interacted with, which offer clues into how they work.
Taking cone snails to the next level
Olivera didn’t go looking for a painkiller. He originally wanted to understand how one particular cone snail, the geography cone, Conus geographus, could lethally attack humans. When he began this work in the 1980s, finding the most potent peptides was a brute force task: purifying venom fractions based on size and polarity; injecting the fractions into mouse brains; determining which fractions elicited interesting behaviors in the mice, such as shaking or slowing; and repeating until left with a 10-40 amino acid-long peptide that was responsible for the behavior (3).
Olivera’s team homed in on a peptide that paralyzed fish by binding to calcium channels found on pain neurons connected to the spinal cord in humans. But they found that the peptide irreversibly blocked the calcium channels, making it a dangerous drug. A more appealing related peptide in a sister species, the magical cone, Conus magus, was reversible, and became the subject of intense drug development. After decades of optimization to improve potency and specificity, Prialt ended up being identical to the original snail peptide. The cone snail’s own design was ultimately best.
Other researchers are now turning to different cone snail species to explore uncharted venom peptides. Helena Safavi-Hemami, a biochemist at the University of Copenhagen who trained with Olivera and now advises Ramiro, is interested in exploring the more than 90 percent of cone snail venom peptides that are still uncharacterized.
“Venoms are these huge libraries of naturally evolved molecules,” said Safavi-Hemami. “They're just fantastic because they're already very specific and selective for their targets.”
She remembers isolating and characterizing one or two peptides at a time during graduate school. Now, she uses higher throughput strategies such as sequencing cone snails’ DNA or RNA to determine the hundreds of peptides they encode. By combining these data with mass spectrometry to measure complex chemical signatures from the peptides, she can better understand the peptides’ chemical characteristics. These technologies also help Ramiro get around one of her main frustrations: collecting enough venom to characterize all of its components through fractionation.
Ramiro studies an intriguing peptide that she discovered in the Philippines in deep water fish-hunting cone snails. She recently published that this peptide mimics the activity of the human hormone somatostatin, which regulates various bodily processes including metabolism and pain (4). The cone snail peptide behaved as a painkiller when injected into mice, reducing pain from heat and surgical incisions.
This could offer a different snail-inspired approach to pain relief than Prialt, Safavi-Hemami said. The somatostatin receptor that Bea’s peptide targets is in peripheral neurons rather than the brain or spinal cord, so it can avoid dealing with the tricky blood-brain barrier.
When Ramiro looked at somatostatin receptor-targeting molecules that researchers had designed in the past for therapeutic purposes, she noticed something interesting. Her cone snail peptide had all the same key features such as chemical modifications and amino acid sequences that make the peptide more stable and selective, showing that evolutionary and lab-based optimizations had arrived at very similar conclusions.
Structures inspired by spiders
Cone snails aren’t the only creatures with peptide-rich venoms, as Hammock knows from personal experience. It has been years since he last traversed deserts at night with a UV light to catch and milk venomous scorpions. Over decades of fieldwork, he has amassed a freezer full of venoms from around the world.
“They are optimized by nature, whether it’s a sea anemone or a scorpion or spider or frog,” Hammock said. “It’s really a goldmine of structures to exploit.”
Identifying the structure of venom proteins is a key step in figuring out how they interact with ion channels or other targets and how they might be modified to optimize the potency and specificity of these interactions. Traditionally, biochemists have used X-ray crystallography to painstakingly construct a three-dimensional model of the peptide. Now, advances in machine learning have led to software like Rosetta and AlphaFold, which can predict a peptide’s structure from its sequence.
Hammock is part of a team at the University of California, Davis, led by Yarov-Yarovoy and Wulff, that uses these computational approaches to make venom peptides into better drugs. Cone snails are not far from their minds. Yarov-Yarovoy and Wulff have snail shells that Olivera gifted them at their desks, but their focus is on a different venomous predator.
As Merck researchers showed decades earlier, the Peruvian green velvet tarantula makes a peptide that blocks the pain-related NaV1.7 sodium channel. The drawback is that it isn’t picky about where it blocks the channel. NaV1.7 and similar channels show up in many key organs such as the heart and brain, and turning them off there could be deadly.
Yarov-Yarovoy and Wulff’s team doesn’t catch their own spiders, though. Using Rosetta software and known structures of the tarantula venom peptide and the ion channel, they make tweaks to the peptide so that it can still bind the NaV1.7 channel as effectively as the original, but with more specificity to neurons. A computational approach means that they don’t need to keep a spider colony in the lab and they can avoid removing spiders from their natural environments to study them.
After designing variations on the peptide, they synthesized it and tested it in isolated neurons and animal models. They recently shared the results of testing the optimized peptides in action in mouse neurons and rats (5). In collaboration with the biotechnology company AnaBios, they have also tested it in human neurons.
But Yarov-Yarovoy and Wulff don’t expect to see their peptides in humans for at least a few more years. For now, their peptide is based on the structure of the tarantula venom, but Yarov-Yarovoy expects that in the future, the algorithms will be able to use just the structure of the ion channel to design a molecule that can effectively block it.
“There will be a learning curve that means nature will still be inspiring us as to what's possible,” Yarov-Yarovoy said. “But we're just starting to go beyond natural peptides and allowing Rosetta to explore on its own.”
Broadening venom’s frontiers
Nearly two decades have passed since Prialt was approved for pain treatment, and it’s been almost four decades since the molecule’s pain-relieving properties were first shown in Olivera’s lab. Yet its success hasn’t been replicated, despite deep-pocketed pharmaceutical companies like Merck and Genentech working on characterizing natural inhibitors of ion channels and their structures.
Hammock has seen firsthand how challenging it can be to bring a pain-relieving drug to clinical trials. His research on insect hormones uncovered a pathway that reduced inflammation and pain in humans. He developed a drug that inhibited a key enzyme, epoxide hydrolase, and showed in many animals — rats, dogs, cats, and even horses — that it blocked pain. Importantly, it seemed to even block neuropathic pain, a particularly tricky variety of pain caused by damaged neurons.
“The large market is inflammatory pain, but the terrifying market is neuropathic pain,” he said. “It’s a field that people run away from.”
Roughly fifty years after Hammock began studying these pathways in mammals, his epoxide hydrolase inhibitor drug completed Phase 1a safety trials in humans last year, clearing it to proceed to Phase 1b (6).
Pain relieving drugs are often limited by differences between animal models and humans, Hammock said. Others like Prialt are stymied by the blood-brain barrier. Wulff hopes that new technologies will help clear these hurdles. Computationally manipulating the structures can help the team design a smaller peptide that is easier to deliver orally and able to cross the blood-brain barrier.
While venom-derived pain relievers creep toward the clinic, technical advances that make venom easier to study have also opened the door to treatments for other diseases. Safavi-Hemami showed that cone snails release an insulin-like peptide in their venom (7). It’s not as unexpected as it might sound. Insulin triggers the uptake of glucose from the blood, so a sudden burst of insulin that clears the bloodstream of fuel could starve a potential prey’s brain and leave it disoriented and vulnerable.
This venom version of insulin has one key difference from the human version that could make a therapeutic difference. While the human version is a hexamer — six interconnected insulin molecules — the snail version is a monomer. That makes it fast-acting, which is useful for the snail to quickly incapacitate its prey, but also could be useful for people who urgently need to regulate their blood sugar levels.
“It was a really beautiful example of taking what nature has evolved and directly using that information to solve a problem that people have tried to solve for a long time,” Safavi-Hemami said.
With venom-producing critters found around the world, studying these venoms’ components also offers a chance to build global capacity for scientific research. Cone snails, for example, are native to the Pacific Ocean, so many studies rely on snails caught in the Philippines. As a student in the Philippines, Ramiro sometimes felt that the lack of resources limited how far she could take her research.
During her training, Ramiro jumped on the opportunity to go to Olivera’s lab to learn how to set up more complex assays. She then returned to the Philippines, where she spent over a year getting the assays up and running and sharing her new knowledge with colleagues.
“It's important that we Filipinos actually get to study whatever we have,” Ramiro said. “We can learn so much from nature.”
- Olivera, B.M. A Serendipitous Path to Pharmacology. Annu Rev Pharmacol Toxicol 61, 9-23 (2021).
- Middleton, R.E. et al. Two tarantula peptides inhibit activation of multiple sodium channels. Biochemistry 41, 14734-47 (2002).
- Olivera, B.M. et al. Purification and Sequence of a Presynaptic Peptide Toxin from Conus geographus Venom. Biochemistry 23 (22), 5087-90 (1984).
- Ramiro, I.B. et al. Somatostatin venom analogs evolved by fish-hunting cone snails: From prey capture behavior to identifying drug leads. Sci Adv 8 (12), eabk1410 (2022).
- Nguyen, P.T. et al. Computational design of peptides to target NaV1.7 channel with high potency and selectivity for the treatment of pain. bioRxiv (2022).
- Hammock, B. et al. Movement to the Clinic of Soluble Epoxide Hydrolase Inhibitor EC5026 as an Analgesic for Neuropathic Pain and for Use as a Nonaddictive Opioid Alternative. J Med Chem 64 (4), 1856-72 (2021).
- Safavi-Hemami, H. et al. Specialized insulin is used for chemical warfare by fish-hunting cone snails. PNAS 112, 1743-8 (2015).